The video below from the Undecided with Matt Ferrell YouTube channel is very interesting. It goes over at least two different ways solid state batteries can be 3D printed. It also covers a brief history of 3D printing.
The video goes over the advantages of 3D printing solid state batteries; mainly the reduction of waste resulting from manufacturing and energy density.
One advantage I would have liked to have seen the video go more into is the advantages of 3D printing solid state batteries of different sizes and shapes. I can see the advantage of "bespoke batteries" in engineering. Not being restricted to cube, cylinder and rectangular geometry would help make certain designs even more compact.
It doesn't look like 3D printing solid state batteries will be a DIY project anyone with a hobby space will be doing any time soon but the thought of ordering custom pyramid-shaped batteries from a company that has the facilities to do it might be something I will do one day.